Hello, I'm considering buying a.

Hello,

I'm considering buying a 2008 Corolla CE with original 34k miles that has had the engine replaced. I'm told by my mechanic, who happens to be the one selling the car that the replacement engine has 42k miles on it and is from a 2010 model. I test drove the vehicle before I knew about the engine swap and did notice a rough idle which has since been taken care of. He's asking $7000 down from the original $7900. The car's passed Maryland State inspection and is in overall good shape. No noticeable leaks, smoke, unusual noises, check-engine lights. Title comes up clean via instaVIN. Still I'm reluctant to pull the trigger on an engine swap car. I dont want to buy problems down the road. What other due diligence should I be conducting to make sure I dont end up with a big problem? What should I be asking about? Anything I need to be aware of regarding the title on an engine swap car either before buying or before selling at some point in the future? Thanks in advance for your help!